Conditioning of thermoplastic compositions for bonding

ABSTRACT

THE BONDING PROPERTIES OF POLYMIDE OR ACETAL THERMOPLASTIC COMPOSITION ARE IMPROVED BY CONDITIONING THE THERMOPLASTIC COMPOSITION PRIOR TO BONDING. CONDITIONERS SUCH AS ISOPROPLY PHENOL OR HEXAFLUOROACETONE SESQUIHYDRATE HAVE BEEN EMPLOYED. CONVENTIONAL EPOXY ADHESIVES THEN ARE EMPLOYED TO BOND THE CONDITIONED THERMOPLASTIC COMPOSITION TO METALLIC AND NON-METALLIC MATERIALS.

United States Patent ABSTRACT OF THE DISCLOSURE The bonding propertiesof polyamide or acetal thermoplastic compositions are improved byconditioning the thermoplastic composition prior to bonding.Conditioners such as isopropyl phenol or hexafluoroacetoneses'quihydrate have been employed. Conventional epoxy adhesives then areemployed to bond the conditioned thermoplastic composition to metallicand non-metallic materials.

for bonding polyamide or acetal thermoplastic compositions to metallicand non-metallic materials.

Other objects, aspects and advantages of this invention will be apparentto one skilled in the art from the following disclosure and appendedclaims.

The conditioners that are employed in the processes of this inventionare isopropyl phenol; 2,4-dimethyl phenol; hexafiuoroacetonesesquihydrate; 1,2-dihydroxybenzene in butyl alcohol orl,3-dihydroxybenzene in butyl alcohol. Generally, the dihydroxybenzenein alcohol mixtures comprise a 1:1 ratio by weight.

The epoxy adhesive that is employed in the processes of this inventionis known in the art. Generally, the epoxy adhesive is a polyepoxideprepared by the reaction of polyhydric alcohols such as glycols,glycerine, trimethylol propane, polyhydric phenols and polyphenols withan excess of an epoxide such as epihalohydrins and alkylene oxides.Preferred polyepoxides are obtained by reacting bisphenol A andepichlorohydrin. This polyepoxide is represented by the formula:

This invention relates to a process for improving the bonding propertiesof thermoplastic compositions. In another aspect, this invention relatesto bonding thermoplastic to metallic and non-metallic materials.

It is well known that thermoplastic compositions usually are notsatisfactorily respective to paints, adhesives, and the like. Generally,preliminary surface modification is required prior to the application ofany commercially available adhesives. For example, U.S. Patent 3,462,335discloses that polymers destined for bonding with an adhesive arebombarded with a stream of an excited inert gas. U.S. Patent 3,235,426discloses a process for rendering polymers receptive to coatings with achemical etching treatment. Various other chemical, mechanical,electrical or thermal pre-treatments are known in the art. However,these prior art processes often are not fully satisfactory. Frequently,these modifications are expensive, time consuming and technicallycomplex. As a result, such processes are not commercially desirable.

It now has been found that the bonding properties of polyamide or atetalthermoplastic compositions are improved by conditioning thethermoplastic composition prior to bonding. Conditioners such asisopropyl phenol have been employed. If desired, the conditioning can becarried out at room temperature for periods of time as short as 10minutes. Conventional epoxy adhesives then are employed to bond theconditioned thermoplastic compositions to metallic materials. Theselection of specific conditioners improves the epoxy bond between thethermoplastic composition and the metallic or non-metallic material.

Accordingly, an object of this invention is to provide a process forimproving the bonding properties of polyamide or acetal thermoplasticcompositions.

Another object of this invention is to provide a process wherein n hasan average value of 0 to 10. Generally, n ranges from 0 to 3, preferably0 to 1. Note, these polyepoxides are characterized as having at leasttwo epoxy groups per molecule. These epoxy resins are further describedin U.S. Patent 3,261,882.

Any metallic material can be employed in the processes of thisinvention. Any of the metals disclosed in the Periodic Table can beemployed as well as combinations thereof. Preferably, aluminum, iron orsteel is employed in the processes of this invention. The metals can bechrome plate if desired. Other substrates, which are nonmetals, also canbe employed. Specific examples include plastic, wood, glass, ceramicsand the like.

Polyamides, which are the condensation polymers of dicarboxylic acidsand diamines, are preferred thermoplastic compositions. Nylon 6/6 or thecondensation polymer of hexamethylenediamine and adipic acid is mostpreferred. Other nylons that can be employed in the processes of thisinvention are disclosed in The Condensed Chemical Dictionary, edited byArthur and Elizabeth Rose, Reinhold Book Corporation, seventh edition,at pages 683 and 684 (1966). Still other polyamides that can be employedin the processes of this invention are disclosed in U.S. Pats. 3,261,882and 3,235,426. Acetal thermoplastic compositions such aspolyoxymethylene are employed in this invention.

The conditioners can be applied to the thermoplastic compositions byvarious means Dipping, brushing and spraying can be employed.Preferably, the thermoplastic compositions were dipped into theconditioner. The thermoplastic compositions then are dried. Preferably,the drying is carried out at ambient room temperature for about tenminutes.

The epoxy adhesive then is applied to the thermoplastic composition andpressed to the metallic material with sufficient force to bond thematerials together. Generally, thermoplastic composition wherein theconditioner is the force is a relatively light load, e.g., about 5 to100 hexafluoroacetone sesquihydrate; and

p.s.i., preferably about 5 to 50 p.s.i. The finished product (b) dryingthe conditioned thermoplastic composition. then is cured at atemperature ranging up to 300 degrees 2. A process according to claim 1wherein the applying Fahrenheit for a time ranging up to 24 hours.Preferably, 5 is carried out by spraying, dipping or brushing and thethe curing temperature ranges up to 250 degrees Fahrendrying is carriedout at room temperature for about heit and the curing time ranges up to5 hours. minutes.

As will be demonstrated, the prior conditioning of the 3. A processaccording to claim 1 wherein the thermothermoplastic compositionprovides improved bonding to plastic compositions are polyamides.various substrates. One application of the processes of this 10 4. Aprocess according to claim 1 wherein the thermoinvention is to bondnylon bobbins (coils) to metal arms plastic compositions are polyamideswhich are the conin activator arm assemblies. Previously, suchassemblies densation product of dicarboxylic acids and diamines. wereunsatisfactory in that the adhesion properties of the 5. A processaccording to claim 1 wherein the thermobobbin surface were poor.Conditioning according to this plasticv compositions are polyamideswhich are the coninvention now has provided desirable bonding betweenthe densation product of adipic acid and hexamethylene dispring-likebobbin and the metal arms. amine.

The advantages of this invention are further illustrated 6. A processfor bonding polyamide or polyoxymethby the following examples. Thereactants and the proporylene thermoplastic compositions to metallic ornon-metaltions and other specific conditions are presented as being licmaterials comprising the steps of: typical and should not be COHStI'l16dto limit the invention 2 (a) applying a conditioner to the bondingurface of the ythermoplastic composition wherein the conditioner isEXAMPLE I hexafluoroacetone sesquihydrate;

(b) drying the conditioned thermoplastic composition; (c) applying anepoxy adhesive comprising a polyepoxide having at least 2 epoxy groupsper molecule to the bonding surface of the thermoplastic composition orto the bonding surface of the metallic or non-met- Various samples wereprepared where nylon bobbins were adhered to metal arms. Some of thesamples were merely bonded with conventional heat conductive epoxyresins. Other samples were conditioned with hexafiuoroacetonesesquihydrate or a 1:1 mixture by weight of 1,3-

dihydroxybenzene in butyl alcohol. The nylon pieces were mhterialidipped into the conditioner and then air dried at ambient p h thebohdlhg ehrfaee 0f the thermopleshc room temperature for 10 minutes. Theepoxy resin was eomposlhoh t0 the hohdlhg Surface 0f the metallic orapplied to the nylon and then firmly pressed to the metal non-metallicmaterial; and arm. The assemblies were cured at 230 degrees Fahrenheit(e) curing the resulting bond.

/o\ (3E3 9H CH; /O\ oHr-wn-orn- -o o o crn-on-cm- ..-o o-om-on-oar(bl-I3 CH3 for 2 hours. When the conditioners were employed, bond 7. Aprocess according to claim 6 wherein the thermostrengths increased froma push-out force (coil pushed plastic compositions are polyamides. offcore) of 15 to 20 pounds to as high as 600 pounds. 8. A processaccording to claim 6 wherein the thermo- This increase reflects theimproved bond strength obtained plastic compositions are polyamideswhich are the conby the use of conditioners. densation product ofdicarboxylic acids and diamines.

9. A process according to claim 6 wherein the thermo- EXAMPLE II plasticcompositions are polyamides which are the con- O her samples wereprepared by bonding strips of nylon densation product of adipic acid andhexamethylene di- 6/ 6 to No. 302 stainless steel strips. The generalprocedure in was the same as that described in Example I except that Aprocess according to claim 6 wherein the metallic only1,3-dihydroxybenzene in butyl alcohol (1:1 mixture material is iron,steel or aluminum. by weight) was employed as the conditioner. Also, the11. A process according to claim 6 wherein the poladhesive in thesesamples was a 1:1 mixture of Epon 828 yepoxide is represented by theformula. and Versamid 125. Epon 828, supplied by Shell Chemical 12. Aprocess according to claim 6 wherein the epoxy Corporation, is a lightcolored, epichlorohydrin-bisphenol adhesive is a 111 IhiXtuI'e y Weightof a condensation A, low molecular weight epoxy resin having the formulaProduct Of eplehlorohydfih and hisphehol A and a previously described.Versamid 125, supplied by General poly mi e r sin. Mills, is a polyamideresin made by the condensation of A Process according to Claim 6 h re te pplying dimerized vegetable oil acids and polyamino compounds. ofSteps and is carried out y p y g, ippi g By bonding two stainless steelstrips to each nylon strip, Or hi g, t e rying Of step (b) is Carriedout at ambia double-lap tensile-shear test specimen was formed. Aftereht room telhpefeiufe for about 10 minutes, the Pressing curing, thetensile test was performed. In the tensile test, of p is carried outul'lder a Pressure f 5 I0 100 the nylon broke and the bond held, therebydemonstrating P- and the curing of p is cafried Out at p the improvedbond strength obtained by the use of conditlll'es ranging P to for atime ranging P to 24 tioners. hours.

Although this invention has been described in consider- A Processaccording to Claim 5 wherein the Pressing able detail, it must beunderstood that such detail is for of p is carried out under a pressuref 5 o 50 the purposes of illustration only and that many variations P-and the curing of p is Carried Out at temperaand modifications can bemade by one skilled in the art hires ranging p to for a time ranging Pt0 5 without departing from the scope and spirit thereof. hours- What isclaimed is: 15. A process according to claim 6 wherein the pressing 1. Aprocess for improving the bonding properties of Of p is earned out underlight Pressure and the polyamide or polyoxymethylene th l ti icuring ofstep (e) is carried out at a temperature of 230 tions comprising thesteps of: F. for 2 hours.

(a) applying a conditioner to the bonding surface of the 75, (Referenceson following page) References Cited UNITED STATES PATENTS Hoppe 156310Groves 156308 Miller 156-307 X Kilduff et a1. 156-308 X Rielly et a1117-47 A 6 3,296,054 1/1967 McCann 156-308 3,556,882 1/1971 Fishman eta1. 11747 A HAROLD ANSHER, Primary Examiner US. Cl. X.R.

